A GXP with a tune is not stock in my book. And if your Fiero runs those times it's not stock either not even close.
Exactly why I mentioned the Fiero - it isn't stock, so whatever performance it may have is as relevant as the numbers you quoted for the non-stock car your friend has.
And I said "a stock GXP with GMPP tune", which is indeed stock in that you can buy a new Solstice with that tune and it is fully warrantable. I agree that any other 'tune' makes it a modified car and into the area where I sense we may agree, comparisons aren't all that meaningful.
They stuff anything they can get their hands on into Fieros, up to and including LS1s. I prefer at least a bit more stockish - I run a 3.2 turbo. I did stuff a 3.4 into an old MG, though, so I guess I'm a swapper too
1957 Jamaican MGA
1958 MGA Twincam
1962 MGA Coupe
1971 Jensen Interceptor
2007 BMW Z4M coupe
2009 Pontiac Solstice GXP Coupe
1965 Jensen CV8
1969 MGC roadster,
1969 Lamborghini Islero S
1988 Pontiac Fiero GT
Bill in BC